Roughening of a metallization layer on a semiconductor wafer

ABSTRACT

A method of manufacturing a semiconductor wafer having a roughened metallization layer surface is described. The method includes immersing the semiconductor wafer in an electrolytic bath. Gas bubbles are generated in the electrolytic bath. A surface of a metallization layer on the semiconductor wafer is electrochemically roughened in the presence of the gas bubbles by applying a reversing voltage between the metallization layer and an electrode of the electrolytic bath.

TECHNICAL FIELD

This disclosure relates generally to the field of semiconductor wafermanufacturing, and in particular to the field of generating a roughenedmetallization layer on a semiconductor wafer.

BACKGROUND

The surface finish of a wafer metallization layer is of importance invarious aspects of semiconductor device manufacturing. While a lowsurface roughness of a metallization layer improves the quality of wirebonding on the metallization layer and facilitates optical inspection ofthe metallized wafer, high roughness is favorable for obtaining highadhesive strength between the metallization layer and an encapsulationapplied during packaging. Therefore, metal deposition parameters as wellas subsequent surface roughening have been considered in the past tocontrol the roughness of a metallization layer surface on a wafer.

SUMMARY

According to an aspect of the disclosure, a method of manufacturing asemiconductor wafer having a roughened metallization layer surface isdescribed. The method comprises immersing the wafer in an electrolyticbath. Gas bubbles are generated in the electrolytic bath. A surface ofthe metallization layer on the wafer is electrochemically roughened inthe presence of the gas bubbles by applying a reversing voltage betweenthe metallization layer and an electrode of the electrolytic bath.

According to another aspect of the disclosure, a semiconductor wafermetallization layer surface roughening equipment comprises anelectrolytic bath. The equipment further comprises a first electrode anda second electrode, the first electrode and the second electrode areconfigured to be connected to a reversing voltage, wherein at least oneof the first electrode and the second electrode is a metallization layeron the wafer. A first gas bubble generator is configured to treat themetallization layer with gas bubbles during electrochemical roughening.

According to still another aspect of the disclosure, a semiconductorpackage comprises a semiconductor die having a metallization layer. Themetallization layer comprises a roughened surface. The semiconductorpackage further comprises an encapsulation embedding at least partiallythe semiconductor die and the roughened surface of the metallizationlayer, wherein the roughened surface has a roughness of a root meansquare height of equal to or greater than 300 nm, 400 nm, 500 nm, 600nm, 700 nm, or 800 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts. The features of the various illustrated embodiments can becombined unless they exclude each other and/or can be omitted if notdescribed to be necessarily required. Embodiments are depicted in thedrawings and are exemplarily detailed in the description which follows.

FIG. 1 is a flowchart schematically illustrating an exemplary method ofmanufacturing a semiconductor wafer having a roughened metallizationlayer surface.

FIG. 2 is a schematic illustration of an anode reaction and a cathodereaction during electrochemical roughening of a metallization layersurface on a wafer in an electrolytic bath.

FIG. 3 is a schematic illustration of an example of an equipment forelectrochemical roughening a metallization layer surface on a wafer.

FIG. 4 is a schematic illustration of another example of an equipmentfor electrochemical roughening a metallization layer surface on a wafer.

FIG. 5 is a schematic illustration of still another example of anequipment for electrochemical roughening a metallization layer surfaceon a wafer.

FIG. 6 is a diagram illustrating an exemplary cross-sectional surfaceprofile having a certain roughness and parameters indicative of theroughness.

FIG. 7 is a plan view image of a metallization layer surface in whichthe surface roughness is illustrated by greyscale and represented byparameters as set out in FIG. 6.

FIG. 8 is an exemplary semiconductor package including a semiconductordie having a roughened metallization layer surface and an encapsulationembedding at least partially the semiconductor die and the roughenedmetallization layer surface.

DETAILED DESCRIPTION

It is to be understood that the features of the various exemplaryembodiments and examples described herein may be combined with eachother, unless specifically noted otherwise.

In many applications metal layers are deposited on semiconductor wafers.The process of depositing one or more metal layers on one or moresurfaces of the wafer is also referred to as applying a metallizationlayer to the wafer or, briefly, as metallizing the wafer. The wafermetallization layer may provide for electrodes (i.e. die pads) on thewafer and/or may provide for an efficient thermal coupling of the waferto a heat sink or other heat dissipation tools.

The semiconductor wafers considered herein may be front-end processed,i.e. integrated circuits (ICs) may be monolithically integrated in eachof the semiconductor wafer regions destined to be cut out of thesemiconductor wafer to form a die. The ICs may represent power ICs,logic ICs, optical ICs, MEMS (micro-electro-mechanical systems) ICs,etc. In particular, the ICs may include or form power transistors, powerdiodes, or other power circuitry.

The generation of the metallization layer may be performed in variousways, e.g. by electroplating (i.e. galvanic deposition) or byelectroless plating (i.e. non-galvanic deposition) or other depositiontechniques. In particular in power applications, the metallization layermay be relatively thick, e.g. may have a thickness of equal to orgreater than 0.5 μm, 1.0 μm, 2.0 μm, 5.0 μm, 10 μm, or 20 μm. Themetallization layer may substantially cover the entire area of one orboth main surfaces of the semiconductor wafer or may cover a part (e.g.equal to or more than or less than 20%, 40%, 60%, 80%) of the area onone or both wafer surfaces.

The metallization layer may be unstructured or structured. If beingstructured, electrodes, die pads, conductive traces, or other conductivemetal structures or patterns may have already been formed out of themetallization layer by, e.g., lithography or processes including, e.g.,resist patterning and/or masking and/or etching, etc.

As mentioned above, surface properties of the metallization layer mayplay an important role in subsequent manufacturing processes and can becontrolled by a variety of parameters. More specifically, the smoothness(or roughness) of a metallization layer surface may be controlled by themetal deposition process as such. Another possibility to control thesmoothness (or roughness) of the metallization layer surface is to applya certain post-treatment to this surface after metal deposition has beencompleted, e.g. a smoothing treatment or a roughening treatment.

At least for certain areas of the metallization layer surface a highdegree of roughness can be desirable. The rougher the surface the betteris the adhesive strength between the metallization layer and otherlayers applied later on to the metallization layer. In particular, ahigh roughness of the metallization layer may improve the adhesivestrength between the metallization layer and organic materials appliedon the metallization layer. Such organic materials may, e.g. be moldcompounds or laminates used for an encapsulation during packaging and/orconductive adhesive materials which may, e.g., be used as an electricalcoupling between the metallization layer and external terminals of asemiconductor package.

Referring to FIG. 1, a method of manufacturing a semiconductor waferhaving a roughened metallization layer surface is described by way ofexample. At S1, the semiconductor wafer is immersed in an electrolyticbath. At S2, gas bubbles are generated in the electrolytic bath. Then atS3, a surface of the metallization layer on the semiconductor wafer iselectrochemically roughened in the presence of the gas bubbles byapplication of a reversing voltage between the metallization layer andan electrode of the electrolytic bath.

As will be described in more detail further below, this process ofwet-chemical roughening of the surface of the metallization layer allowsto enhance the roughness of the surface to achieve a degree of roughnesswhich is considerably higher than known from conventional rougheningprocesses. Further, the process of wet-chemical roughening describedherein provides for a high degree of controllability and reproducibilityof the obtained surface properties (in particular the roughness of thesurface). Further, the roughening treatment described herein iscompliant with conventional semiconductor processing and can thereforebe implemented in the wafer manufacturing process without any majorobstacles.

FIG. 2 is an illustration of chemical reactions taking place at an anodeA and at a cathode C during electrochemical roughening in an electrolyte230 of an electrolytic bath. The anode A is electrically coupled to apositive potential of a reversing voltage power supply 250, while acathode C is electrically coupled to a negative potential of thereversing voltage power supply 250. Since the reversing voltage powersupply 250 provides for reversing polarity (i.e. for an alternatingcurrent flowing through the electrolytic bath), FIG. 2 represents a“snapshot”, i.e. when reversing the voltage output at the reversingvoltage power supply 250 the anode A in FIG. 2 becomes the cathode C andthe cathode C in FIG. 2 becomes the anode A. The electrolyte 230 at thecathode C and the electrolyte 230 at the anode A are electricallycoupled by schematically indicated coupling 240 to allow an electriccurrent flow. The coupling 240 may be implemented by the electrolyte 230contained in a (common) electrolytic bath or by an electrical connectorconnecting the electrolyte 230 at the cathode C with the separatedelectrolyte 230 at the anode A.

In FIG. 2 both the anode A and the cathode C are formed by metallizationlayers 212 and 222 on semiconductor wafers 210 and 220, respectively.When biased as an anode A, metal of the metallization layer 212 isremoved from the metallization layer 212 (see the arrows pointing awayfrom 212) and dissolved in the electrolyte 230. On the other hand, metalfrom the electrolyte 230 is deposited to the same amount on themetallization layer 222 of the wafer 220 biased as a cathode (see thearrows pointing towards 222). After reversal of the polarity at thereversing voltage power supply 250, the process reverses at thesemiconductor wafers 210, 220, i.e. metal from the electrolyte 230 isdeposited on the metallization layer 212 of the wafer 210 and metal fromthe metallization layer 222 of the wafer 220 is removed and transferredinto the electrolyte 230.

Generally, the metallization layer(s) 212, 222 may be based on a metalor a metal alloy of, e.g., Cu, Ni, NiP, Au, Zn, Al, etc. In thefollowing, for the purpose of explanation and without loss ofgenerality, Cu is used as an example of the metal of the metallizationlayer. The wafer(s) 210, 220 may comprise or be of a semiconductormaterial such as, e.g., Si, SiC, SiGe, GaAs, GaN, AlGaN, InGaAs, InAlAs,etc.

Further, as indicated in FIG. 2, the cathode reaction and (optionally)the anode reaction is carried out in the presence of gas bubbles 260.The gas bubbles 260 impede a uniform deposition of metal at the cathodeC, thereby creating the desired roughness of the surface of themetallization layer 222. Metal deposition at the cathode C may, e.g.,also be partly or completely a metal re-deposition, since, e.g.,virtually all deposited metal may have been removed from themetallization layer 222 during the time before when the metallizationlayer 222 was biased as an anode A.

The uniformity of the roughness can be controlled by the gas bubbles260. The smaller the average size of the gas bubbles 260, the better isthe uniformity of the roughness. Differently put, gas bubbles 260 mayact to form a temporary and statistically distributed micro-masking ofthe surface of the metallization layer 222 during the electrochemicaldissolution and deposition process on the surface of the metallizationlayer 222.

Generally, the uniformity of the roughness obtained by using a stream ofgas bubbles 260 in the immediate vicinity of the surface of themetallization layer 222 is significantly better than the uniformity of a“natural” surface roughness which may occur in a conventionalelectrolytic bath. As known in the art, the generation of such “natural”roughness at a surface of the metallization layer 222 can be preventedby specific additives, which are usually added to the electrolytic bathto avoid the generation of such “natural” surface roughness. The“natural” surface roughness (obtained without gas bubbles and withoutadditives) is caused by variations in the conditions of themetallization layer surface which result in different deposition rates.It is characterized by a high degree of inhomogeneity and thereforecannot be used for the purposes described herein, e.g. for reliablyimproving the adhesive strength between the roughened metallizationlayer and, e.g., an encapsulation.

While FIG. 2 exemplifies both electrodes (the anode A and the cathode C)to be implemented by metallization layers 212, 222 of wafers 210, 220,respectively, it is also possible that only one electrode is formed by awafer metallization layer, while the other electrode is implemented byother means, e.g. by a metal plate immersed in the electrolytic bath. Inthis case, by virtue of the polarity reversal of the reversing voltagepower supply 250, the same processes as illustrated in FIG. 2 take placeat the metallization layer of the wafer and the same results areachieved. The metal plate forming the other electrode does not even haveto be made of the metal of the (wafer) metallization layer but may bemade of an inert electrode material, since the process described hereinmay, e.g., completely rely on the re-deposition of metal (during thecathode reaction) which has been previously removed from themetallization layer (during the anode reaction).

More specifically, the entire electrochemical roughening process may beperformed without any depletion of metal ions in the electrolyte 230. Incontrast to conventional electrochemical deposition processes, in whichthe electrolyte is depleted during deposition and therefore needs to beregenerated from time to time, electrolyte regeneration is not requiredduring electrochemical roughening as described herein.

Differently put, the concentration of metal ions (of the metal of themetallization layer(s) 212, 222) in the electrolyte 230 may be constantover time (i.e. no depletion and no enrichment of metal ions in theelectrolyte 230 over the entire process, in particular e.g. at any timeduring the process). Constant metal ion concentration may be achieved byapplying a reversing voltage configured to set the anode reaction andthe cathode reaction to equal rates.

The gas used to generate the gas bubbles 260 may be an inert gas or anoxidizing gas or a reducing gas or a mixture of any of those gases.Inert gases such as, e.g., N₂ or Ar merely exert a “masking effect” onthe deposition (or re-deposition) of the metal during the cathodereaction. “Masking effect” means that each bubble 260 locally preventsdeposition (or re-deposition) of metal at the location where the gasbubble 260 is temporarily in contact with the surface of themetallization layer 222.

Reducing gases such as, e.g., N₂H₂, CO or oxidizing gases such as, e.g.,air or O₂, further act as a reaction agent during the cathode reactionand (optionally) during the anode reaction. In the cathode reaction thegas reacts with the metal which has just been deposited on the surface.Metal oxide secondary products (if an oxidizing gas is used) will beincorporated in the metallization layer 222 near its surface. Forinstance, if an oxidizing gas is used, it is possible that the surfaceof the metallization layer 222 is locally and partly or even completelyinsulated by the creation of punctual or extensive and/or continuousareas of metal oxide.

An extensive and continuous layer of metal oxide may even form aninsulating layer on the roughened surface of the metallization layer 222which may completely cover and electrically insulate the metallizationlayer 222. In other words, in addition to the effect of uniformlyroughening the surface of the metallization layer 222, the gas bubbles260 may further be used to generate functionalized surface(s) of themetallization layer(s) 212, 222.

Further, there is the option to mask certain areas of the metallizationlayer before emerging the wafer in the electrolytic bath so as toprevent roughening of the masked areas. As the roughening processdescribed herein may be carried out in a material-neutral manner, i.e.the roughening process does not require any additional metal materialfor deposition, the mean metallization layer thickness may remainunchanged and/or the masked smooth areas and the roughened areas mayremain on the same average level.

Further, the approach of masking may also or additionally be appliedwithin the concept of functionalizing the surface of the metallizationlayer 222. That is, it is possible that, e.g., a first mask is used todefine a pattern of smooth and roughened surface areas and/or a secondmask is used to define a pattern of chemically functionalized andnon-functionalized surface areas of the metallization layer 222. To thisend, it may be possible to first roughen the surface of themetallization layer without functionalizing the roughened surface areasand then to apply a second mask (which may be different from the firstmask) to the pre-roughened surface in order to functionalize certainareas of the pre-roughened surface of the metallization layer 222.

In this and other cases, it is possible that a plurality of differentgases is used during the roughening process. For instance, if a patternof functionalized surface areas is to be created, the process may startwith the introduction of an inert gas for roughening withoutfunctionalizing the surface and may then, e.g. after a masking step,continue with e.g. an oxidizing gas or a reducing gas forfunctionalizing the unmasked portions of the roughened surface.

FIGS. 3 to 5 illustrate various examples of an equipment forelectrochemical roughening a metallization layer surface on asemiconductor wafer. All process features and variants described abovemay be applied to any of the examples of FIGS. 3 to 5. Further, specificfeatures of the process or the equipment for roughening a metallizationlayer surface as disclosed in the following description can be combinedwith any of the features disclosed in conjunction with the descriptionof FIGS. 1 and 2 or other examples throughout this specification.

Referring to FIG. 3, an equipment 300 for roughening a metallizationlayer surface 222 on a semiconductor wafer 220 comprises an electrolyticbath 330 containing the electrolyte 230. A first electrode 310 and asecond electrode 320 are immersed in the electrolytic bath 330. Thefirst electrode 310 and the second electrode 320 are configured to beconnected to a reversing voltage from a reversing voltage power supply250. At least one of the first electrode 310 and the second electrode320—in the example of FIG. 3 the second electrode 320—is themetallization layer 222 on the semiconductor wafer 220. Further, theequipment 300 includes a first gas bubble generator 350 which isconfigured to treat the metallization layer 222 with gas bubbles 260during electrochemical roughening.

The first gas bubble generator 350 may be configured to generate astream or “curtain” of fine gas bubbles 260 from a gas flow obtained viaa supply line 352 connected to a gas reservoir (not shown). The firstgas bubble generator 350 may comprise or be a gas diffusor. The gasdiffusor may include a gas diffusor nozzle panel configured to generatea dense gas bubble stream across a sufficiently large cross-sectionalarea in the electrolytic bath 330. The dense gas bubble stream may havea cross-sectional area sufficient large to completely embed themetallization layer 222 on the wafer 220.

As shown in FIG. 3, the metallization layer 222 on the wafer 220 may bestructured. If the metallization layer 222 is structured in separatedareas 2221, 222_2, the separated areas 222_1, 222_2 may be electricallyconnected. For example, the electrical connection between the area 222_1of the metallization layer 222 and the area 222_2 of the metallizationlayer 222 may be provided by an underlying electrically conductive layer322, e.g. a seed layer used during the metallization process.

The reversing voltage (e.g. an AC voltage) between the metallizationlayer 222 and the electrode 310 of the electrolytic bath 330 may beapplied over a number of cycles. The cycle duration (which is theduration between consecutive reversals of the power supply) may be equalto or greater than 5 s, 10 s, 20 s, 30 s, or 40 s. The number of cyclesmay be equal to or greater than 5, 10, or 20. The voltage may, e.g., bein a range of 1 to 10 V, in particular 1.5 to 5 V and more in particular2 to 4 V.

That is, a certain current I or a certain voltage U is predetermined fora certain period τ (cycle duration) during which the cathode reaction iscarried out at one of the electrodes (e.g. in FIG. 3 the secondelectrode 320). Then, the voltage is reversed and the anode reaction iscarried out for, e.g., the same period of time T. The current or thevoltage during the anode reaction may be of the same amount than duringthe cathode reaction.

The voltage reversal may be periodical. The reversing voltage powersupply 250 may be an AC (alternating current) power supply. Thereversing voltage frequency used by the reversing voltage power supply250 may, e.g., be equal to or less than 1 Hz, 0.5 Hz, 0.2 Hz, 0.1 Hz,0.05 Hz, or 0.02 Hz.

While in FIG. 3 the orientation of the wafer 220 may be parallel to thedirection of the gas bubble stream, it is also possible that thesemiconductor wafer 220 is held inclined relative to the direction ofmovement of the gas bubbles 260 in the electrolytic bath 330. Aninclined orientation of the semiconductor wafer 220 relative to thestream of gas bubbles 260 is illustrated in FIG. 4 illustrating anotherequipment 400 for electrochemical roughening a metallization layersurface on a semiconductor wafer 220.

Further, still referring to FIG. 4, the metallization layer 222 may bepositioned in a region of the electrolytic bath 330 where the gasbubbles 260 render the electrolytic bath 330 foamy. As foam formationmay mostly occur near the surface of the electrolytic bath 330, thewafer 220 may be positioned near the surface of the electrolyte 230 ofthe electrolytic bath 330. Therefore, in contrast to conventionalwet-chemical electrolytic applications, where foam formation needstypically to be avoided, surface roughening in accordance with thisdisclosure may specifically use the formation of foam to support theroughening process.

It has been observed that the more foam is formed in the electrolyte 230the higher is the degree of roughness which can be achieved. Hence, theroughening process may be carried out as a “foam roughening method” inwhich the roughening is achieved in the presence of a gas bubble foam ofthe electrolyte 330. Optionally, a foaming agent may be added to theelectrolyte 230 to increase foam formation.

FIG. 5 illustrates a further equipment 500 for electrochemicalroughening a metallization layer surface on a semiconductor wafer. Theequipment 500 includes an electrolytic bath 330 as previously described,and reference is made to the above description in order to avoidreiteration. The equipment 500 may further include one or more holders510, 520 for suspending a plurality of semiconductor wafers 210, 220 inthe electrolytic bath 330. For instance, a number of equal to or greaterthan N wafers 210, 220 may be processed simultaneously, with N being aninteger equal to or greater than, e.g., 2, 4, 8, 10, . . . , while inthe example of FIG. 5 there is N=8.

As illustrated in FIG. 5, the equipment 500 may be symmetrical in termsof the anode/cathode reaction and/or the placement of the semiconductorwafers 210, 220 and/or the generation of gas bubble streams in thepresence of the semiconductor wafers 210, 220. Hence, the equipment 500may include a second gas bubble generator 550 which may be positionedbeneath the semiconductor wafer(s) 210. The second gas bubble generator550 is configured to treat the metallization layer on the furtherwafer(s) 210 with gas bubbles 260 during electrochemical roughening. Thesecond gas bubble generator 550 may be designed the same way asdescribed above for the first gas bubble generator 350.

Further, a stirrer 560 may be provided in the electrolytic bath 330 formoving and intermixing the electrolyte 230.

In FIG. 5 and throughout all examples, the entire electrochemicalroughening process may be performed in a material-neutral way, i.e.without loss of metal material at the electrodes (in FIG. 5 the wafer(s)210 and wafer(s) 220). In total, no metal ions may be removed from theelectrolyte 230, since the rate of the metal-depleting anode reactionand the rate of the metal-depositing cathode reaction may be the same.That way, the roughening processes described herein may provide for ahigh homogeneity of roughness which can be obtained without any loss ofmetallization layer material. These conditions are usually not met byconventional roughening processes which rely on chemical etching orlaser treatment. Further, surface functionalization as described aboveis not available by such conventional approaches.

FIG. 6 is a diagram illustrating the surface profile of a metallizationlayer having a certain roughness. The surface profile is depicted versusa sample length L. Sz denotes the maximum height of the surface profile.Sp denotes the maximum height of the peaks of the surface profile. Svdenotes the maximum height of valleys of the surface profile.

FIG. 7 illustrates an exemplary greyscale image of the surface roughnessof a Cu metallization layer prior to the roughening treatment asdescribed herein. The following parameters in accordance with thestandard ISO 25178 (Geometric Product Specifications—Surface Texture)were measured:

Sa=88.456 nm,

Sp=367.43 nm,

Sq=111.41 nm,

Sv=512.52 nm and

Sz=879.95 nm.

Sa is the arithmetic mean height of the surface profile. Sq is the rootmean square height of the surface profile.

As known in the art, Sq may be used as a measure of surface roughness.That is, the greater the value of Sq the rougher is the surface.

The initial roughness can be greatly enhanced by the metallization layersurface roughening process described herein. According to one example, aCu metallization layer was applied to a wafer and the following heightparameters were measured in accordance with ISO 25178:

Sa=33.8 nm,

Sq=65.3 nm,

Sz=23435 nm,

Sp=2849 nm,

Sv=20586 nm,

Ssk=−15.1, and

Sku=7282.

According to ISO 25178, Ssk denotes the skewness of the surface and Skudenotes the kurtosis of the surface.

After a roughening treatment of the metallization layer using a voltageof 5 V, a polarity reversal time of T=20 s and a number of C=10 cycles,the following roughness parameters were obtained:

Sa=494 nm,

Sq=622 nm,

Sz=21508 nm,

Sp=3919 nm,

Sv=17589 nm,

Ssk=0.0394, and

Sku=3.60.

As may be seen from a comparison of Sq prior to and after the rougheningtreatment, the exemplary roughening process enhanced the roughness ofthe Cu surface nearly by a factor of 10.

Neither such enhancement of roughness nor the absolute values of theparameters (in particular of Sq) disclosed herein are known to beachieved by conventional roughening treatments available in the art.

FIG. 8 illustrates an exemplary semiconductor package 800. Thesemiconductor package 800 includes a semiconductor die 810 having atleast one metallization layer 222. The semiconductor package 800 furtherincludes an encapsulation 850 embedding at least partially thesemiconductor die 810 and the roughened surface of the metallizationlayer 222. The roughened surface of the metallization layer 222 has aroughness of a route means square height (Sq) of equal to or greaterthan 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, or 800 nm (in accordancewith ISO 25178).

The semiconductor die 810 may be a power die, e.g. a die including oneor more power transistors and/or one or more power diodes or other powerICs. The metallization layer 222 may, e.g., include a die backsidemetallization layer 222. The die backside metallization layer 222 may bea load electrode metallization layer of the power die 810, e.g. a drainelectrode metallization layer or a source electrode metallization layer.

As illustrated in FIG. 8, the metallization layer 222 may optionallyconnect to a heat sink 860. The heat sink 860 may be exposed from theencapsulation 850. In other embodiments the metallization layer 222 may,e.g., form an external terminal of the semiconductor package 800 and maydirectly connect to external circuitries, e.g. to conducting traces on aPCB (printed circuit board).

The roughened surface of the metallization layer 222 may be confined topartial areas of the overall surface of the metallization layer 222,e.g. to areas in which the (roughened) surface of the metallizationlayer 222 directly engages with the encapsulation 850. In other words,in other areas, e.g. in the area where the heat sink 860 is connected tothe metallization layer 222, the surface of the metallization layer 222may have been kept smooth by, e.g., masking during the rougheningprocess.

The semiconductor die 810 may further include other metallization layerswhich have also been at least partly roughened by any of the processesdescribed herein. By way of example, the semiconductor die may beequipped with a first separated area of metallization layer 222_1 (e.g.a load electrode metallization layer 222_1) and a second separated areaof metallization layer 2222 (e.g. a gate metallization layer 222_2). Inother words, the metallization layer 222 may be separated in a pluralityof disjointed metallization layer areas. Also, these metallizationlayers 222_1, 2222 may have been processed to have roughened surfaceareas at least in regions covered by the encapsulation 850.

Hence, the metallization layers 222 and/or 222_1 and/or 2222 may furthercomprise a smooth surface (e.g. in the central part of thesemetallization layers), wherein the roughness of the roughened surface isequal to or greater than 5, 7, 9 or 11 times the roughness of the smoothsurface in terms of the root mean square height (Sq) of the respectivesurfaces.

Further, the semiconductor package 800 may include a roughened surfaceof a metallization layer 222 and/or 222_1 and/or 222_2, which mayinclude metal oxide secondary products or metal halides secondaryproducts. These secondary products are an unavoidable consequence of afunctionalized metallization layer surface created by using eitheroxidizing or reducing gases during the roughening process.

The following examples pertain to further aspects of the disclosure:

Example 1 is a method of manufacturing a semiconductor wafer having aroughened metallization layer surface, the method comprising immersingthe wafer in an electrolytic bath; generating gas bubbles in theelectrolytic bath; and electrochemically roughening a surface of themetallization layer on the wafer in the presence of the gas bubbles byapplying a reversing voltage between the metallization layer and anelectrode of the electrolytic bath.

In Example 2, the subject matter of Example 1 can optionally includewherein the gas is an inert gas or an oxidizing gas or a reducing gas ora mixture of any of these gases.

In Example 3, the subject matter of Example 1 or 2 can optionallyinclude wherein the gas bubbles are configured to form a temporary andstatistically distributed micro-masking of an electrochemical dissolveand deposition process on the metallization layer surface.

In Example 4, the subject matter of any preceding Example can optionallyinclude wherein the metallization layer is positioned in a region of theelectrolytic bath where the gas bubbles render the electrolytic bathfoamy.

In Example 5, the subject matter of any preceding Example can optionallyinclude structuring the metallization layer into separated areas beforeimmersing the wafer in the electrolytic bath, wherein the separatedareas are electrically connected.

In Example 6, the subject matter of any preceding Example can optionallyinclude masking certain areas of the metallization layer beforeimmersing the wafer in the electrolytic bath so as to prevent rougheningof the masked areas.

In Example 7, the subject matter of any preceding Example can optionallyinclude wherein the reversing voltage between the metallization layerand the electrode of the electrolytic bath is applied over a number ofcycles, wherein the cycle duration is equal to or greater than 5 s, 10s, 20 s, 30 s, or 40 s and/or the number of cycles is equal to orgreater than 5, 10, or 20.

In Example 8, the subject matter of any preceding Example can optionallyinclude wherein the reversing voltage frequency is equal to or less than1 Hz, 0.5 Hz, 0.2 Hz, 0.1 Hz, 0.05 Hz, or 0.02 Hz.

In Example 9, the subject matter of any preceding Example can optionallyinclude wherein the metallization layer is based on copper.

Example 10 is a semiconductor wafer metallization layer surfaceroughening equipment, including an electrolytic bath; a first electrodeand a second electrode, the first electrode and the second electrode areconfigured to be connected to a reversing voltage, wherein at least oneof the first electrode and the second electrode is a metallization layeron the wafer; and a first gas bubble generator configured to treat themetallization layer with gas bubbles during electrochemical roughening.

In Example 11, the subject matter of Example 10 can optionally includewherein the wafer is held inclined relative to a direction of movementof the gas bubbles in the electrolytic bath.

In Example 12, the subject matter of Example 10 or 11 can optionallyinclude wherein the first electrode and the second electrode are eachmetallization layers on different wafers, further comprising: a secondgas bubble generator configured to treat the metallization layer on thefurther wafer with gas bubbles during electrochemical roughening.

Example 13 is a semiconductor package, including a semiconductor diehaving a metallization layer, the metallization layer comprising aroughened surface; and an encapsulation embedding at least partially thesemiconductor die and the roughened surface of the metallization layer,wherein the roughened surface has a roughness of a root mean squareheight of equal to or greater than 300 nm, 400 nm, 500 nm, 600 nm, 700nm, or 800 nm.

In Example 14, the subject matter of Example 13 can optionally includewherein the subject matter of any one of Examples 9 to 11 can optionallyinclude wherein the metallization layer further includes a smoothsurface, and wherein the roughness of the roughened surface is equal toor greater than 5, 7, 9, or 11 times the roughness of the smooth surfacein terms of the root mean square height of the respective surfaces.

In Example 15, the subject matter of Example 13 or 14 can optionallyinclude wherein the semiconductor die is a power die and themetallization layer comprises a power die backside metallization layerand/or a load electrode metallization layer of the power die.

In Example 16, the subject matter of any of Examples 13 to 15 canoptionally include wherein the roughened surface comprises metal oxidesecondary products or metal halides secondary products.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method of manufacturing a semiconductor waferhaving a roughened metallization layer surface, the method comprising:immersing the semiconductor wafer in an electrolytic bath; generatinggas bubbles in the electrolytic bath; and electrochemically roughening asurface of a metallization layer on the semiconductor wafer in thepresence of the gas bubbles by applying a reversing voltage between themetallization layer and an electrode of the electrolytic bath.
 2. Themethod of claim 1, wherein the gas bubbles are generated from an inertgas or an oxidizing gas or a reducing gas or a mixture of any of thesegases.
 3. The method of claim 1, wherein the gas bubbles are configuredto form a temporary and statistically distributed micro-masking of anelectrochemical dissolve and deposition process on the surface of themetallization layer.
 4. The method of claim 1, wherein the metallizationlayer is positioned in a region of the electrolytic bath where the gasbubbles render the electrolytic bath foamy.
 5. The method of claim 1,further comprising: structuring the metallization layer into separatedareas before immersing the semiconductor wafer in the electrolytic bath,wherein the separated areas are electrically connected.
 6. The method ofclaim 1, further comprising: masking certain areas of the metallizationlayer before immersing the semiconductor wafer in the electrolytic bathso as to prevent roughening of the masked areas.
 7. The method of claim1, wherein the reversing voltage between the metallization layer and theelectrode of the electrolytic bath is applied over a number of cycles,wherein the cycle duration is equal to or greater than 5 s, 10 s, 20 s,30 s, or 40 s and/or the number of cycles is equal to or greater than 5,10, or
 20. 8. The method of claim 1, wherein a frequency of thereversing voltage is equal to or less than 1 Hz, 0.5 Hz, 0.2 Hz, 0.1 Hz,0.05 Hz, or 0.02 Hz.
 9. The method of claim 1, wherein the metallizationlayer is based on copper.
 10. A semiconductor wafer metallization layersurface roughening equipment, comprising: an electrolytic bath; a firstelectrode and a second electrode, the first electrode and the secondelectrode are configured to be connected to a reversing voltage, whereinat least one of the first electrode and the second electrode is ametallization layer on a semiconductor wafer; and a first gas bubblegenerator configured to treat the metallization layer with gas bubblesduring electrochemical roughening.
 11. The semiconductor wafermetallization layer surface roughening equipment of claim 10, whereinthe semiconductor wafer is held inclined relative to a direction ofmovement of the gas bubbles in the electrolytic bath.
 12. Thesemiconductor wafer metallization layer surface roughening equipment ofclaim 10, wherein the first electrode and the second electrode are eachmetallization layers on different semiconductor wafers, furthercomprising: a second gas bubble generator configured to treat themetallization layer on the further semiconductor wafer with gas bubblesduring electrochemical roughening.